Analyzer Sample System Design Basics for Selecting the Right Options
by Morgan Zealear, on 3/2/21 8:45 AM
In the chemical, petroleum, energy, and semiconductor industries, fluid sampling and analysis require a wide range of sampling system designs. Accurate representative samples are essential in monitoring process conditions, product quality, and in maintaining environmental compliance. Whether you’re installing a grab sampling system for a new production process or upgrading an aging sampling system, proper design and option selection are critical to a consistent, reliable sampling process.
Accurate sampling begins with a clear understanding of the purpose of the analysis, the process fluid and conditions, and any limitations of infrastructure surrounding the sampling station. System design can range from the relatively simple to the very complex, including:
- Low-pressure, non-toxic liquid sampling by an operator who manually opens and closes a valve to dispense the liquid into a glass or polyethylene bottle
- High-pressure, high-temperature hydrocarbons that require cooling and filtering before filling a pressurized cylinder to transport a sample to the analyzer
Between those two ends of the sampling spectrum, there’s a near-infinite variety of design decisions and options to tailor a grab sampling system to the specific requirements of the sampling process. And when determining the best grab sampling system design it’s often to seek expert guidance.
To give you an appreciation for the options involved in designing an analyzer sample system, let’s review some of the critical decisions that you’ll make and how they impact system design.
Cylinder or Bottle? Depends on Process Fluid and Pressure
Sample container selection is based on process fluid and pressure. Glass or polyethylene jars are appropriate for low-pressure, non-toxic samples. An optional septum cap on the jar reduces the chances of leakage or off-gassing during sampling and transport to the analyzer.
Metal cylinders are the best option for toxic and/or high-pressure samples. They eliminate the risk of spillage or off-gassing during the sampling process and transport to the analyzer. You also have the option of including a rupture disk or relief valve to avoid accidents caused by overpressuring the vessel. This is for sample fluids subject to increased temperature during transportation to the analyzer.
Depending on the process fluid, you may also need to treat the surfaces of transport tubing and cylinder inside surfaces to reduce sample fluid absorption and adsorption into metallic surfaces and provide a more representative sample. Here, you have the option of electropolishing, and coatings such as SilcoNert®, Silcolloy®, and Dursan®.
Sample Station Location
In many retrofit implementations, the distance between the sample tap and the sampling station can be considerable, especially when the sampling station can’t be located close to the tap because of safety, ergonomic, or obstructing infrastructure considerations. When the sampling station is a significant distance from the sample tap consider options such as:
- installing a heat trace to keep fluids from cooling to the point where the flow is impeded;
- purging the transport line before and/or after taking the sample to remove stagnant fluid from the transport line; or
- using a continuous flow design to ensure fresh process fluid is readily available and sample time is minimized.
Safe and Efficient Sampling Processes
Any sampling process must be safe, efficient, and consistent. All design options should be made with these goals in mind. Let’s look at some of the key options to consider regarding analyzer sample system design.
Manual vs. Fixed-Volume
For toxic or high-pressure process fluids, you may want to opt for a fixed-volume sampling method. Rather than depending on the operator to manually control the level of sample fluid in the container, the fixed-volume option isolates the process pressure from the operator and limits the volume of dispensed fluid which helps prevent accidental overfilling. This is ideal for liquid or gas samples whose volume can be affected by increased temperature during transport.
Standard vs. Continuous Flow
A standard sampling configuration delivers process fluid to a container from the sample tap. Before taking the sample, the transport line retains stagnant fluid that could compromise sample quality. To prevent this, the transport line needs to be purged before taking the sample. The length of the transport line (tap to sampling station), volume, and flow rate determine how much time is required to purge the transport line. An accurate calculation of lag time to remove stagnant fluid is an essential aspect of sampling system design. So, the longer the line, the longer the amount of time required for the purge and the overall sampling process.
An alternative (and more efficient design) is a continuous flow configuration. It continuously circulates process fluid from a positive-pressure location through a sample cylinder and returns it to the process at a lower-pressure location while the operator takes a sample. There’s no waiting to purge the transport line or fill a container. When the sample cylinder is ready to be removed, a bypass valve redirects the flow away from the cylinder.
Continuous flow configuration circulates process fluid through the sample cylinder.
Although a continuous flow configuration is a more complex design, it can be a better option from the perspective of reduced sample time, particularly when a sample station is distant from the sample tap.
Analyzer Sample System Design Options? Work With Experts
You may have in-house expertise for designing and assembling grab sampling systems, but I’ve found that companies that work with experienced grab sampling vendors achieve better results regarding system design, implementation, and operations. The benefits include:
- designing systems to carefully accommodate existing infrastructure;
- recommending the highest quality components;
- simplifying the sampling process; and
- minimizing the time required to safely capture a representative sample.
For companies that don’t have in-house expertise, there’s all the more reason to seek the guidance of experts. Considering the time you might spend assessing the need, developing the design, and assembling a system, the entire process will be all the more efficient when you work with an expert. The overall result is an analyzer sample system designed to deliver long-term reliability, efficiency, and consistency.
Swagelok Field Engineers have been working with process and quality professionals in Northern California industries on analyzer sample system designs with options carefully tailored to the unique requirements of each sampling process. Our Field Engineers bring a wealth of experience to help customers assess design and performance, especially in high-risk process environments. We help identify improvement opportunities, whether via the latest component options or a new sample system design.
To find out more about how Swagelok Northern California can assist you with analyzer sample system design and selection of options that reliably deliver representatives samples, contact our team today by calling 510-933-6200.
Morgan Zealear | Product Engineer – Assembly Services
Morgan holds a B.S. in Mechanical Engineering from the University of California at Santa Barbara. He is certified in Section IX, Grab Sample Panel Configuration, and Mechanical Efficiency Program Specification (API 682). He is also well-versed in B31.3 Process Piping Code. Before joining Swagelok Northern California, he was a Manufacturing Engineer at Sierra Instruments, primarily focused on capillary thermal meters for the semiconductor industry (ASML).